Re: New importdata function testing

[Jordi Gutiérrez Hermoso]

On 21 October 2012 12:07, Rik <address@hidden> wrote:
> 10/20/12
>
> Erik,
>
> I did just a small test with importdata and it doesn't seem to work as
> expected.
>
> For a file, I used import.tst containing
>
> 1,2,3
> 4,5,6
>
> And then in Octave, I used
> importdata ('import.tst', ',')
> warning: unrecognized escape sequence '\S' -- converting to 'S'

Oops, my bad:

     http://hg.savannah.gnu.org/hgweb/octave/rev/9a455cf96dbe#l2.365

> I am also concerned that the implementation reads the entire file into a
> string and then uses a number of for loops and regexp which will be slow in
> Octave.  I did a benchmark with the following:
>
> x = rand (1e4, 10);
> dlmwrite ('tst.csv', x, ',')
> tic; y = dlmread ('tst.csv', ','); toc
> Elapsed time is 0.209933 seconds.
> tic; y = importdata ('tst2.csv', ','); toc
> Elapsed time is 3.2 seconds.
>
> I believe it would be faster  to have importdata check the header lines
> only and then pass off the work to dlmread if possible.  dlmread is written
> in C++ and, per the benchmarking above, is very fast.

It would be preferrable if we could write some minimum common subset
of this family of functions as a C++ function and leave the rest in
m-file language. I consider writing code in C++ a last resort for
optimisation at the very high cost of making the code less
understandable for most people. Many of our users are scared by C++,
but any Octave user understands the m-file language.

- Jordi G. H.